Ferrofluidic seals and bearings are known in the art and are described in U.S. Pat. Nos. 3,612,630 and 4,526,382. FerroFluid Film Bearings (FFFBs) use a magnetic oil, a ferrofluid, as a lubricating oil and use magnetic seals to maintain the oil inside the bearing.
Typically, FFFBs are utilized in a spindle assembly to support a spindle axis. The magnetic oil directly lubricates the spindle axis as it rotates within the FFFB; to do this, the magnetic oil is maintained within the FFFB through the action of a pair of magnetic seals.
To fill a FFFB of a spindle assembly with magnetic oil, the spindle axis is first placed into the FFFB. A vacuum is then generated in the volume of the FFFB and afterward, the magnetic oil is allowed to fill the FFFB. Any magnetic oil between the magnetic fields of the magnetic seals will remain within the FFFB. If the amount of magnetic oil within the magnetic field of a first one of the magnetic seals does not precisely match the amount within the magnetic field of a second magnetic seal, the oil will be attracted towards the second magnetic seal and will then spread outside of the second magnetic seal. To prevent this from happening, the entirety of the oil which is outside of a predetermined location in each magnetic seal is removed.
For FFFBs internal to a machine, the access to a magnetic seal internal to the machine is not free and therefore, the magnetic oil can not be removed to a predetermined location.
Ferrofluidics Corporation of Nashua, New Hampshire produces a spindle assembly with a single FFFB. The FFFB supports a large portion of the spindle axis and thus, a large amount of magnetic oil is needed to fill the volume between the magnetic seals.